1. Field of the Invention
The present invention relates to injection molding. More particularly, the present invention relates to hot runner nozzles.
2. Related Art
In injection molding, hot runners are used to deliver molding material (melt) from a molding machine, which typically has an injection screw to plasticize the molding material, to a mold cavity, which is typically cooled to solidify the molding material. The purpose of the hot runner is to keep the molding material within an allowable temperature range as the molding material is injected from the molding machine to the mold cavity. Typically, the temperature of the molding material at or near the mold gate is critical. Problems can arise if the gate temperature is unsuitable for the molding material. For example, if the gate temperature is too low, the mold cavity may not completely fill; if the gate temperature is too high, the molding material may string or drool (i.e., leak) from the mold gate.
The gate temperature depends on a myriad of factors, such as properties of the molding material used, the mold cavity temperature, geometric features that the molding material navigates (e.g., gate diameter), and settings of heaters in the hot runner. Some of these factors, such as the molding material used, cannot usually be changed, while others, such as the settings of the heaters in the hot runner, can be changed easily.
In an ideal situation, an injection molding operator simply sets one or more heaters in the hot runner to obtain a gate temperature that yields molded products of satisfactory quality. If a problem such as stringing occurs, the operator can many times simply dial down a hot runner nozzle heater temperature to compensate. If a mold cavity does not fill properly, the operator may choose to increase the nozzle temperature. However, situations do arise where controlling the heater cannot obtain a gate temperature that eliminates a problem. And in many of these situations it is very difficult, if not impossible, to change another factor to achieve a satisfactory gate temperature.